U.S. patent number 5,842,095 [Application Number 08/868,919] was granted by the patent office on 1998-11-24 for image forming device with multiple image forming units.
This patent grant is currently assigned to Fuji Xerox Co., Ltd.. Invention is credited to Atsuyuki Kitamura.
United States Patent |
5,842,095 |
Kitamura |
November 24, 1998 |
Image forming device with multiple image forming units
Abstract
The invention relates to a device for packaging and applying
makeup, the device includes a rigid elongate tubular body open at
one end and having an inside space suitable for containing makeup,
and an applicator suitable for being received in the body. The
applicator includes a stalk provided at one end with a makeup
applicator element and secured at its other end to a handle that
has a cap suitable for closing the opening of the body in which the
applicator element is engaged. A throat is formed in the body for
wringing out the applicator element while the applicator is being
withdrawn. The device further includes a moving wall defining the
inside space, at least in part, and capable of moving in response
to a change of pressure in the space caused by the applicator being
withdrawn. While the device is in use, the moving wall is subjected
on the outside to atmospheric pressure.
Inventors: |
Kitamura; Atsuyuki (Ebina,
JP) |
Assignee: |
Fuji Xerox Co., Ltd. (Tokyo,
JP)
|
Family
ID: |
15836239 |
Appl.
No.: |
08/868,919 |
Filed: |
June 4, 1997 |
Foreign Application Priority Data
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Jun 6, 1996 [JP] |
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8-166705 |
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Current U.S.
Class: |
399/299;
399/381 |
Current CPC
Class: |
G03G
15/0194 (20130101); G03G 2215/0119 (20130101) |
Current International
Class: |
G03G
15/01 (20060101); G03G 015/01 () |
Field of
Search: |
;399/297,298,299,300,301,303,381,388,394,395 |
References Cited
[Referenced By]
U.S. Patent Documents
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|
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5363178 |
November 1994 |
Matsumoto |
5386286 |
January 1995 |
Kinouchi et al. |
5455668 |
October 1995 |
De Bock et al. |
5537195 |
July 1996 |
Sagara et al. |
5581327 |
December 1996 |
Izumizaki et al. |
5602633 |
February 1997 |
Yoshida et al. |
5623719 |
April 1997 |
De Cock et al. |
|
Foreign Patent Documents
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5-53412 |
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Mar 1993 |
|
JP |
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7-287455 |
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Oct 1995 |
|
JP |
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7-319254 |
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Dec 1995 |
|
JP |
|
Primary Examiner: Brase; Sandra L.
Attorney, Agent or Firm: Oliff & Berridge, PLC
Claims
What is claimed is:
1. An image-forming device comprising:
a plurality of image-forming units disposed along a copy material
transport path, wherein said plurality of image-forming units
sequentially copies toner images onto a copy material moving along
said copy material transport path;
transport copying means for each image-forming unit for
transporting said copying material while being placed in contact
with an image retention body and so that toner images are copied
from said image retention body onto said copy material;
entry-side transporting means disposed upstream from said plurality
of image-forming units along said copy material transport path;
and
exit-side nip transporting means disposed downstream from said
plurality of image-forming units along said copy material transport
path, wherein a relationship S'>2A, A+B, A+C is fulfilled,
wherein: A is the interval separating each of said plurality of
image-forming units along said copy material transport path; B is
the interval between one of the plurality of said image-forming
units that is positioned furthest upstream, and said entry-side nip
transporting means; C is the interval between one of the plurality
of said image-forming units which is positioned furthest downstream
and said exit-side nip transporting means; and S' is the length of
a minimum-size copy material along the direction of transport,
wherein when said copy material is not being nipped by either said
entry-side or said exit-side nip transporting means then said copy
material spans and is nipped by at least a plurality of said
transport copying means of said image-forming units.
2. An image-forming device comprising:
means for supporting and transporting copy materials moving along a
copy material transport path and supporting a copy material;
a plurality of image-forming units disposed along said copy
material transport path, wherein said plurality of image-forming
units sequentially copies toner images onto said copy material
moving along said copy material transport path;
transport copying means for each image-forming unit at a position
corresponding to an image retention body so that said copy material
is transported and put in contact with said image retention body
and a toner image on said image retention body is copied onto said
copy material;
entry-side nip transporting means disposed upstream from said
plurality of image-forming units along said copy material transport
path; and
exit-side nip transporting means disposed downstream from said
plurality of image-forming units along said copy material transport
path, wherein a relationship S'>2A, A+B, A+C is fulfilled,
wherein: A is the interval separating each of said plurality of
image-forming units along copy material transport path; B is the
interval between one of said plurality of image-forming units that
is positioned furthest upstream and said entry-side nip
transporting means; C is the interval between one of said plurality
of image-forming units which is positioned furthest downstream and
said exit-side nip transporting means; and S' is the length of a
minimum-size copy material along the direction of transport,
wherein when said copy material is not being nipped by either said
entry-side or said exit-side nip transporting means then said copy
material spans and is nipped by at least a plurality of said
transport copying means of said image-forming units.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image-forming device that uses
electrophotography. In particular, the present invention relates to
an improvement in image-forming devices wherein a plurality of
image-forming units is disposed along a copy-material transport
path and toner images are copied one after another from the
plurality of image-forming units to the copy material moving along
the copy-material transport path.
2. Description of Related Art
An example of known technology in the field of color image-forming
devices involves the "tandem" method. In this technology, a
plurality of image-forming units are disposed along a horizontal
paper transport path. As the paper moves along the paper transport
path, the image-forming units transfer toner images onto the paper
one by one to form a color image on the paper.
The tandem method of transporting the paper can use a copy roll
that is disposed on each image-forming unit so that it comes into
contact with a photosensitive body used for image retention. This
photosensitive body and the copy roll is used to transport the
paper (see, for example, Japanese Laid-open Publication Number
7-319254).
In another method, a belt is used to transport the paper (as in
Japanese Laid-open Publication Number 5-53412). In this method, a
paper transport belt circulates along the paper transport path. The
paper is supported by the paper transport belt using electrostatic
adhesion.
Also, different methods for arranging the image-forming units have
been proposed. In one method, a plurality of image-forming units
are disposed in a horizontal row along a horizontal paper transport
path (see, for example, Japanese Laid-open Publication Number
5-53412). In another method, the image-forming units are disposed
in a vertical row along a vertical paper transport path (see, for
example, Japanese Laid-open Publication Number 7-287455).
However, in conventional copy roll transport methods, if the
dimension separating the copy rolls of the image-forming units is
wide enough, it is possible for the transport force to be applied
only by the nipping between a single photosensitive body of an
image-forming unit and the copy roll. The nip pressure between the
photosensitive body and the copy roll cannot be set too high
because it is necessary to take copying properties into
consideration in addition to the paper transport properties. This
results in a greater tendency for the paper to be fed diagonally
(i.e., skewing).
Also, when the paper is passing through the copy position of an
image-forming unit, and a lengthy section has already passed, the
end of the paper can become curled, or unstable. This causes
variations in the positioning of the end of the paper to the copy
position for the next image-forming unit and results in shifts in
the starting position at which the toner images for each color
element are written to the paper. This leads to color offsets and
uneven color distribution.
Furthermore, when the paper is transported solely by the nipping of
the photosensitive body of the image-forming unit and the copy
roll, unevenness in the thickness of the toner layer at the copying
positions of the image-forming units occurs. This tends to produce
variations in the speed of the paper as it passes the copy
positions of the image-forming units and leads to color shifts and
uneven color in the color image.
In conventional image-forming devices that use a paper transport
belt, the position at which the end of the paper enters the copy
positions of the image-forming units is more stable than those
devices using copy rolls. The paper transport belt limits uneven
color distribution along the direction of paper transport. However,
as the paper transport belt moves, "walking" may take place (i.e.
the paper transport belt may move back and forth along the width
axis of the belt). Thus, the color image may show color shifts and
uneven color distribution in the direction perpendicular to the
paper transport direction (i.e., the width direction).
The present invention solves the problems in the technology
described above and provides a more compact image-forming device
that restricts color shifts and uneven color distribution from
irregularities in the transport of the copy material.
SUMMARY OF THE INVENTION
According to a first preferred embodiment of the invention, a
transport copying means for each image-forming unit comes into
contact with an image retention body. Entry-side and exit-side nip
transporting means are disposed upstream and downstream from the
image-forming units, respectively. The distance between entry-side
and the exit-side nip transporting means is shorter than the length
of a standard-size copy material. Thus, the copy material can
always be nipped and transported by entry-side and/or exit-side nip
transporting means. This allows the copy material to be transported
through the copy positions of the image-forming units at a constant
speed and at a consistent entry position.
Thus, it is possible to limit the shifting and unevenness in the
color that accompanies inconsistencies in the transport operations
without using means for supporting and transporting copy materials
such as a copy material transport belt. The device is also more
compact.
In the present invention, the color material transport path can be
substantially vertical and the image-forming units can be in a
vertical row. This configuration provides short image-forming units
and also allows the means for feeding copy material to be
positioned under the image-forming units to provide a more compact
package.
If copy material is transported with the copying means of the
image-forming units, there may be a concern that gravity may cause
problems when the copy material transport path is substantially
vertical. However, the copy material is always nipped and
transported by the entry-side and/or exit-side nip transporting
means and, therefore, the copy material is always transported
without being affected by gravity.
According to a second preferred embodiment of the present
invention, a transport copying means is positioned in contact with
an image retention body of each image-forming unit and the
entry-side and exit-side nip transporting means are disposed
upstream and downstream of the image-forming units. Therefore, a
minimum-size copy material that is not being nipped by either
entry-side or exit-side nip transporting means will be nipped by at
least a plurality of transport copying means of the image-forming
units. Thus, even if a minimum-size copy material is used, the copy
material can be transported in a stable manner without a means for
supporting and transporting the copy materials such as a copy
material transport belt. This makes it possible to limit the shifts
and unevenness in color from inconsistencies in the transport of
the copy material. The device is also more compact.
In a third preferred embodiment of the present invention, copy
material is supported and transported using means for supporting
and transporting copy materials. Entry-side and exit-side nip
transporting means are disposed upstream and downstream from the
image-forming units, respectively. The distance between the
entry-side and exit-side nip transporting means is shorter than the
length of standard-size copy material. Thus, the copy material is
always nipped by entry-side and/or exit-side nip transporting means
and if the means for supporting and transporting "walks" (moves
side to side gradually), the copy material is kept from moving side
to side. Thus, shifts and unevenness in color from inconsistencies
in the transport of the copy material are prevented, and the device
can be easily made more compact.
Furthermore, according to a fourth preferred embodiment of the
present invention, copy material is supported and transported using
means for supporting and transporting copy materials. Transport
copying means is disposed on each image-forming unit at a position
corresponding to an image retention body so that the copy material
is transported and put in contact with the image retention body and
so that a toner image on the image retention body is copied onto
the copy material. Entry-side and exit-side nip transporting means
are disposed upstream and downstream from the image-forming units,
respectively. When the copy material is not being nipped by either
the entry-side or the exit-side nip transporting means, the copy
material is nipped by at least a plurality of transport copying
means of image-forming units and the means for supporting and
transporting copying materials "walks" (moves side to side
gradually), the minimum-size copy material is kept from moving side
to side. Thus, shifts and unevenness in color that accompany
inconsistencies in the transport of the copy material are
prevented, and the device can be easily made more compact.
Furthermore, since a paper guide is disposed between the paper
transport belt and the fixing device, greater compactness can be
achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1(a) is a cross-sectional plan view of a first preferred
embodiment of the image-forming image-forming device of the present
invention;
FIG. 1(b) is a cross-sectional plan view of a second preferred
embodiment of the image-forming device of the present
invention;
FIG. 2 is another cross-sectional plan view of the image-forming
device according to the first preferred embodiment;
FIG. 3(a) is a cross-sectional plan view of an image-forming unit
used in the first preferred embodiment;
FIG. 3(b) is an enlarged cross-sectional plan view of the
photosensitive cartridge of the image forming unit of FIG.
3(a);
FIG. 4 is a plan view of the paper transport system of the first
preferred embodiment;
FIG. 5 is a plan view of the paper transport system when a
standard-size paper is used in the image-forming device according
to the first preferred embodiment;
FIG. 6 is a plan view of the paper transport system when a
minimum-size paper is used in the image-forming device according to
the first preferred embodiment; and
FIG. 7 is a cross-sectional plan view of the image-forming device
according to a second preferred embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the first preferred embodiment shown in FIG. 1(a) the following
conditions are required: S'>2A, A+B, A+C, where: A is the
interval between the plurality of image-forming units 2 along the
copy material transport path 1; B is the interval between the
image-forming unit 2a, which is positioned furthest "upstream" in
transport path 1, and the entry-side nip transporting means 6; C is
the interval between the "downstream" image-forming unit 2d and the
exit-side nip transporting means 7; and S' is the length along the
transport direction of a minimum-size copy material 3. Therefore,
if the copy material 3 is not being nipped by either the entry-side
nip transporting means or the exit-side nip transporting means 7,
then it is nipped by at least a plurality of transport copying
means 5 of image-forming units 2.
Dimension A is preferably uniform for all image-forming units 2
(2a-2d). However, it is also possible for some or all of the
intervals to have different dimensions. If some or all of the
intervals between image-forming units 2 have different dimensions,
then the following conditions must be fulfilled: S'>A1+A2,
A2+A3, A1+B, A3+C, where: A1is the interval A between image-forming
units 2a and 2b; A2 is the interval A between image-forming units
2b and 2c; and A3 is the interval A between image-forming units 2c
and 2d.
In the second preferred embodiment shown in FIG. 1(b), copy
material support-transport means 8 is positioned and moves along
copy material transport path 1. The copy material support-transport
means 8 supports copy material 3. A plurality of image-forming
units 2a-2d is arranged along the copy material transport path 1.
In this image-forming device, the copy material 3 moves along the
copy material transport path 1, and the plurality of image-forming
units 2 to transfer toner images onto the copy material 3 one after
another. Entry-side nip transporting means 6 and exit-side nip
transporting means 7 are positioned upstream and downstream from
the plurality of image-forming units 2, respectively. Copy material
3 is transported in a nipped state by nip transporting means 6,
7.
To reliably prevent transport discrepancies of standard-size copy
material 3: a distance L along copy material transport path 1
between entry-side and exit-side nip transporting means 6, 7 must
be shorter than a length S of standard-size copy material 3 (e.g.,
an A4-size copy material, as set in the JIS (Japan Industrial
Standard) standards.
The copy material support-transport means 8 can comprise a
transport belt or a gripper. If a gripper is used, it is necessary
to temporarily retract the gripper during passage through the
copying positions of the image-forming units 2 to prevent
interference. Therefore, a transport belt is preferable.
It is crucial that the copying means applies transport pressure to
copy material 3, therefore, copying means is not restricted to a
transport copying means 5 comprising a copy roll, but can also
comprise an alternative device such as a copying corotron.
As shown in FIG. 1(b), a transport copying means 5 is disposed on
each of the plurality of image-forming units 2 at a position that
corresponds to image retention body 4. Transport copying means 5
serves to transport the copy material 3 toward the image retention
body 4 and to transfer the toner image on the image retention body
4 to the copy material 3.
To provide good transport characteristics for a minimum-size copy
material 3, the relations S'>2A, A+B, A+C are required, where: A
is the interval between the plurality of image-forming units 2
along the copy material transport path 1 (see FIG. 1(a)); B is the
interval between image-forming unit 2a, which is positioned
furthest upstream on the transport path, and entry-side nip
transporting means 6 (see FIG. 1(a)); C is the interval between
image-forming unit 2a, which is positioned furthest downstream, and
exit-side nip transporting means 7 (see FIG. 1 (a)); and S' is the
length of the minimum-size copy material 3 (see FIG. 1(a)). When
the copy material 3 is not being nipped by either entry-side or
exit-side nip transporting means 6, 7, the copy material 3 must be
pinched while spanning at least a plurality of transport copying
means 5 of image-forming units 2. As in the structure shown in FIG.
1(a), dimension A is generally set identically between
image-forming units 2a-2d, but it would also be possible to set one
or all of the intervals differently.
In the operation of the first preferred embodiment of the invention
shown in FIG. 1(a), a standard-size copy material 3 (with a length
S) is nipped by entry-side nip transporting means 6 and/or
exit-side nip transporting means 7. When this happens, the
standard-size copy material 3 receives transport force mainly from
the nip transporting means 6, 7 and passes the copy positions of
each image-forming unit 2. Since span A between the copy positions
of image-forming units 2 is short, the entry position of the end of
the copy material 3 to a copy position of an image-forming unit 2
is uniform, thus providing a stable speed at which the copy
material 3 passes over the copy positions of the image-forming
units 2.
In FIG. 1(a), if S'>2A, A+B, A+C, then even if a minimum-size
copy material 3 (with a length S') is not being nipped by either
nip transporting means 6 or 7, it would still be nipped and
transported by at least a plurality of transport copying means 5 of
the image-forming units 2.
In the second preferred embodiment of the invention shown in FIG.
1(b), a standard-size copy material 3 (with a length S) is
transported by copy material support-transporting means 8 through
the copy positions of image-forming units 2. Further, the copy
material 3 is also transported by the entry-side nip transporting
means 6 and/or the exit-side nip transporting means 7. Thus, even
if the copy material support-transporting means 8 "walks", the
displacement of the copy material 3 along its width axis would be
prevented by the entry-side nip transporting means 6 and/or the
exit-side nip transporting means 7.
If, in FIG. 1(b), S'>2A, A+B, A+C, then even if minimum-size
copy material 3 (with a length S') is not nipped by either nip
transporting means 6 or 7, it would still span across and be nipped
by a plurality of transport-copying means 5 of the image-forming
units 2. Thus, the copy material 3 is transported in a stable
manner without any skewing.
FIG. 2 shows another cross-sectional view of the first preferred
embodiment of the color image-forming device of the present
invention. Image-forming units 22 (specifically, 22a-22d) for four
colors (in the preferred embodiment: yellow, magenta, cyan, and
black) are arranged in a vertical row within housing 21. Below
these is a paper-feeding cassette 23, in which paper is stored. A
paper transport path 24 is disposed vertically along positions
corresponding to the image-forming units 22.
Starting from the upstream position of paper transport path 24, the
image-forming units 22 (22a-22d) form the yellow, magenta, cyan,
and black toner images. There is also a photosensitive cartridge
30, a laser exposure device 40, and a copy roll 50.
As shown in FIG. 3, a photosensitive cartridge 30 is formed
integrally from the following elements: a drum-shaped
photosensitive body 31; a charge roll 32, for charging the
photosensitive body 31; a developer 33 using a corresponding color
toner to develop an electrostatic latent image that is formed on
the charged photosensitive body 31 by the laser exposure device 40;
and a cleaner 34, for removing the residual toner on the
photosensitive body 31.
In this embodiment, the developer 33 is positioned below the
photosensitive body 31 and has a developer housing 331 that extends
laterally. Developer housing 331 holds a developing agent (a
single-component developing agent comprising a non-magnetic
developing agent or a magnetic developing agent) containing a
prescribed color toner. A pair of developing agent agitating
members 332 is disposed within the developer housing 331, and a
developing roll 333 is disposed near the opening that faces the
photosensitive body 31. A developing agent feeding member 334 is
disposed near developing roll 333 to feed the developing agent in
the developer housing 331 to the developer roll 333. Further, there
is a thickness regulating member 335 for regulating the thickness
of the developing agent on developing roll 333.
A cleaner 34 is disposed above the photosensitive body 31 and
includes a cleaner housing 341 that extends laterally. A blade 342
on the cleaner housing 341 scrapes residual toner where it faces
photosensitive body 31.
In this first preferred embodiment, the developer housing 331,
which holds the developing agent, and the cleaner housing 341,
which retrieves residual toner, are extended laterally to provide
storage space and to provide a short photosensitive cartridge
30.
In the laser exposure device 40, a case 41 holds a semiconductor
laser (not shown in the drawing), a polygon mirror 42, an
image-forming lens 43, and mirrors 44 and 45. A light from the
semiconductor laser is deflected and scanned by the polygon mirror
42. The resulting light is guided to form an exposure on the
photosensitive body 31 via the image-forming lens 43 and the
mirrors 44 and 45. The case 41 extends laterally to stay short.
Furthermore, the copy roll 50 is positioned separate from the
photosensitive cartridge 30 and is placed in contact with the
photosensitive body 31 of the photosensitive cartridge 30. The copy
roll 50 is rotated in synchronization with the photosensitive body
31 by a drive transfer system not shown in the drawing. A
prescribed electric field is applied to the copy roll 50 so that a
transfer force is applied to the copy roll 50 that corresponds to
the toner image on the photosensitive body 31. It is also possible
to have the copy roll 50 assembled integrally with the
photosensitive cartridge 30.
In this embodiment, a paper-feeding cassette 23 is positioned on a
feed roll 61 to feed paper at a prescribed timing as shown in FIG.
2 and FIG. 4. An entry-side nip transport roll 62 is positioned on
a paper transport path 24 between the feed roll 61 and the
image-forming unit 22a, that is furthest upstream. An optical
paper-pass sensor 63 is disposed below the entry-side nip transport
roll 62.
A paper-pass sensor 63 detects the end of the paper. It is possible
to have the detection timing from the sensor be the basis for the
timing at which the laser exposure devices 40 of the image-forming
units 22 record electrostatic latent images.
Further, a fixing device 64 is disposed on paper transport path 24
above the image-forming unit 22d.
The fixing device 64 includes: a heating roll 641 and a pressure
belt 642, which forms large contact nipping area with heating roll
641. This structure provides a larger nipping area than a pair of
rolls and therefore, improves the fixing properties. The fixing
device 64 also functions as an exit-side nip transport roll 65.
An ejection roll 66 is disposed downstream from the fixing device
64 to take up the paper. The paper that is taken up is then held in
a holding tray 67 formed on top of the housing 21.
In this embodiment, the following relationships are
established:
where, referring to FIG. 4: L is the distance between the
entry-side nip transport roll 62 and the exit-side nip transport
roll 65; A is the interval between the image-forming units 22 along
paper transport path 24; B is the interval between the
image-forming unit 22a, which is furthest upstream, and the
entry-side nip transport roll 62; C is the interval between the
image-forming unit 22d, which is furthest downstream, and the
exit-side nip transport roll 65; and S is the length of a
standard-size paper 25 (i.e., A4 paper based on JIS standards); and
S' is the length of minimum-size paper (in this embodiment, A6
postcard size based on JIS standards).
Further, paper guides 71-75 are disposed before the image-forming
unit 22a, which is furthest upstream, between the image-forming
units 22a-22d, and past the image-forming unit 22d, which is
furthest downstream. Paper guides 71-75 regulate the motion path of
the paper.
Tapered guide surfaces 76 are formed on paper guides 71-74, which
are positioned in front of the image-forming units 22a-22d. The
tapered guide surfaces 76 are sloped slightly to the right from
vertical and are extended in a direction that keeps them always in
contact with the back surface (including the end) of the paper
being copied and transported. The paper is kept in contact with the
tapered guide surfaces 76 while it is moved toward the nipping area
between the photosensitive body 31 and the copy roll 50. The paper
path is set so that the end of the paper comes into contact with
the photosensitive body 31 right before reaching the nipping
area.
The paper guide 75 positioned past image-forming unit 22d, which is
the furthest downstream, is divided in two to form a tapered guide
surface 77 that is sloped slightly to the left of vertical and an
arcuate guide surface 78 that is connected to the tapered guide
surface 77 and oriented toward the nipping area of the fixing
device 64. The end of the paper is, thereby, prevented from curling
when it passes the image-forming unit 22d, and is reliably guided
to the nipping region of the fixing device 64.
The following is a description of the operation of a color
image-forming device based on this embodiment. First, a case
involving a standard-size paper 25 (with a length S) is described.
An image-formation start switch not shown in the drawing is
pressed, and the paper 25 in the paper-feed cassette 23 is fed out
by the feed roll 61. The end of paper 25 then reaches the
entry-side nip transport roll 62. Paper 25 is then nip-transported
by the entry-side nip transport roll 62 and is projected in
sequence to the copy positions of the image-forming units 22a-22d
along the paper transport path 24. The transport speed of the paper
25 is kept constant by the entry-side nip transport roll 62 so that
the speed at which the paper passes the copy positions of the
image-forming units 22a-22d is also kept constant.
Span A between the copy positions of the image-forming units
22a-22d and span B between the entry-side nip transport roll 62 and
the copy position for the image-forming unit 22a are kept short
relative to standard-size paper. Thus, as the paper 25 enters the
copy positions for the image-forming units 22a-22d, its end region
is supported by the entry-side nip transport roll 62 or the
copy-nipping sections (the nipping section between photosensitive
body 31 and copy roll 50) of the image-forming units 22a-22c and
the position of the end of paper 25 as it enters the copy positions
for image-forming units 22a-22d is stabilized. This maintains
constant entry timing as paper 25 enters the copy positions for the
image-forming units 22a-22d and prevents offsets in the copy
positions for the different color toner images, preventing shifts
in the color of the images, and preventing uneven distribution of
color.
When the end of paper 25 reaches and is nipped at the fixing device
64 (exit-side nip transport roll 65), the paper 25 is nipped and
transported by both the entry-side nip transport roll 62 and the
exit-side nip transport roll 65. Then, as the paper 25 is
transported further, the nipping action by the entry-side transport
roll 62 is disengaged. However, since the paper 25 is being nipped
and transported by exit-side nip transport roll 65, the transport
speed stays constant. Thus, the speed at which paper 25 passes the
copy positions of image-forming units 22a-22d remains constant.
Then, when paper 25, on which the toner image has not been fixed,
passes all the way through fixing device 64 so that the toner image
is fixed, it is ejected to the holding tray 67 (see FIG. 2) by the
ejection roll 66.
The following is a description of a case where a minimum-size paper
25 (with a length S') is used (see FIG. 4 and FIG. 6). An
image-formation start switch (not shown in the drawings) is pressed
and the paper (postcard) 25 is inserted from a manual insertion
tray (not shown in the drawings) by the feed roll 61. The end of
paper 25 then reaches the entry-side nip transport roll 62.
Then, paper 25 is nipped and transported by the entry-side nip
transport roll 62 and enters the copy positions for the
image-forming units 22a-22d along the paper transport path 24. Due
to the dimensions of paper 25, the nipping operation performed by
the entry-side nip transport roll 62 is disengaged when paper 25
passes across the image-forming unit 22b. However, the paper 25
always stays nipped and transported by at least two image-forming
units 22. Also, if the paper 25 is a thick paper such as a
postcard, the nipping pressure at the copy-nipping sections is
greater so that the paper 25 can be transported in a stable manner,
without any skewing, past the copy positions for the image-forming
units 22a-22d, where the toner images are copied onto the paper
25.
When the paper 25 reaches the fixing device 64 (exit-side nip
transport roll 65), the paper 25 is nipped and transported by the
exit-side nip transport roll 65, and the unfixed toner images are
fixed. Then, the paper 25 is ejected by the ejection roll 66 into
the holding tray 67 (see FIG. 2).
The paper transport path 24 is disposed vertically, and the
image-forming units 22 (22a-22d) are arranged in a vertical row.
Thus, the height of the housing 21 is kept small. Further, since
the paper-feed cassette 23 is disposed below the image-forming unit
22, the extra space requirements for paper-feed cassettes that
project externally are avoided. Thus, a compact device can be
easily provided.
Since image-forming units 22, or more specifically, photosensitive
cartridge 30 and laser exposure device 40, are short and four
levels can be arranged in a vertical row without an excessively
large height.
If the paper transport path were disposed horizontally and the
image-forming units were disposed in a horizontal row, it would be
necessary to decrease the horizontal dimension of the
photosensitive cartridge 30 and the laser exposure device 40.
However, if the housing for the developer or the cleaner is formed
with a larger height, a more complex structure is required for the
developing agent to be fed or the developing agent to be cleaned by
the cleaner. Also, in laser exposure device 40, the polygon mirror
must be horizontal to stably drive the polygon mirror and,
therefore, creates an obstacle to minimizing the horizontal
dimension.
In the second preferred embodiment shown in FIG. 7, the color
image-forming device includes image-forming units 22 (22a-22d) for
four colors identical to the first embodiment will be assigned like
numerals and detailed descriptions will be omitted. A circulating
paper transport belt 80 is disposed along a vertical paper
transport path 24. An electrostatic adhesion roll (not shown in the
drawing) electrostatically adheres the paper to the paper transport
belt 80, and then the paper is transported through the copy
positions of the image-forming units 22 (22a-22d). A belt cleaner
81 for removing paper particles on paper transport belt 80 is also
shown.
In this second preferred embodiment, the copy rolls 50
corresponding to the photosensitive bodies 31 of the image-forming
units 22 (22a-22d) are disposed on the back surface of the paper
transport belt 80. The copy roll 50 and the photosensitive body 31
nip and support the paper on the paper transport belt 80.
Unlike the first embodiment, this embodiment does not require paper
guides along paper transport path 24. A paper guide 79 is disposed
solely between the paper transport belt 80 and the fixing device 64
to guide the paper to the nipping region of the fixing device
64.
The entry-side nip transport roll 62, the copy-nipping sections
(the nip sections between the copy rolls 50 and the photosensitive
bodies 31) of the image-forming units 22, and the relative
positioning (relative dimensions) of the exit-side nip transport
roll 65 along the paper transport path 24 are the same as the first
embodiment.
The following is a description of the operation of the color
image-forming device of the second preferred embodiment. In this
description, a standard-size paper is used. The paper is
transported by the paper transport belt 80 through the copy
positions of the image-forming units 22 (22a-22d). The paper is
always nipped and transported by either the entry-side nip
transport roll 62 or the exit-side nip transport roll 65. Thus,
even if the paper transport belt 80 "walks", the paper on transport
belt 80 does not walk.
Thus, the "walking" of the paper transport belt 80 does not affect
the paper on the paper transport belt 80, and the paper is able to
move along the transport direction at a fixed speed. This allows
the color toner images from image-forming units 22 to be layered
without offset, thereby resulting in a color image without any
shifting or unevenness.
When a minimum-size paper is used, it is supported by the copy-nip
section of at least two image-forming units 22. Thus, even if the
paper transport belt 80 "walks", the paper on paper transport belt
80 does not, and shifting along the width axis is prevented.
Therefore, with minimum-size paper, color toner images from
image-forming units 22 can be layered without offsets, thereby
providing a color image without any shifting or unevenness.
In this technology, image-forming units 2a-2d can comprise any type
of unit as long as they form toner images for each color component
and retain the images on an image retention body 4. However, it is
preferable to have the peripheral parts for the image retention
body 4 to take the form of cartridges as much as possible for ease
of installation.
Also, the image retention body 4 can comprise any type of body that
can retain a toner image. Any appropriate material corresponding to
the means for forming latent images can be used, such as a
photosensitive body or a dielectric. The form taken by the image
retention body 4 is not specified, and can be drum or
belt-shaped.
The form of the transport copying means 5 is not specified as long
as it can copy a toner image to the copy material 3 while applying
a transport force to the copy material 3. However, it is preferable
to use a copy roll to which a copying electric field is applied for
simplicity and compactness.
Further, referring to FIG. 1(a), there is no need to have anything
disposed in front of the image-forming units 2 if the copy material
3 is transported by the transport copying means 5 of the
image-forming units 2a-2d. However, to provide a more stable
transport of the copy material 3, it is preferable to dispose the
copy member guides 9 in front of the image-forming units 2a-2d so
that the copy material 3 is guided between the image retention body
4 and the transport copying means 5.
The direction in which the image-forming units (2a-2d) are arranged
can correspond with the arrangement of the copy material transport
path 1. For example, if the copy material transport path 1 is
disposed in a substantially horizontal orientation, then the
image-forming units 2 would need to be arranged sideways. If the
copy material transport path 1 is disposed in a substantially
vertical orientation, then the image-forming units 2 would need to
be arranged vertically. In this case, it is preferable to position
the copy material transport path 1 in a substantially vertical
orientation, and to have the image-forming units 2 arranged
vertically to keep the device compact.
Any structure can be used for the entry-side and exit-side nip
transporting means 6, 7 as long as the transport force applied by
the nip pressure can reliably transport the copy material 3 in the
transport direction. There is no problem in having separate means
for each function, but it is preferable to have the exit-side nip
transporting means 7 also serve as the fixing means to simplify
structure.
The fixing means can take on various forms including a pair of
fixing rollers and a combination of a fixing roller and a fixing
belt.
The specific sequence in the arrangement of image-forming units
(2a-2d) is not specified, but it is preferable for the last
image-forming unit to form the black toner image to maintain image
quality in a monochrome-black mode.
While this invention has been described with the specific
embodiments outlined above, many alterations, modifications and
variations are apparent to those skilled in the art. Accordingly,
the preferred embodiments described above are illustrative and not
limiting. Various changes may be made without departing from the
spirit and scope of the invention as defined in the following
claims.
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